During the operation of any machine having slidably engaged metal surfaces, friction consumes energy. In the lubricant and bearing arts, there is a continuous effort directed at developing various ways of reducing the coefficients of static and dynamic friction between such surfaces and thereby minimizing these losses. The arts have progressed to the stage where a gain of a few percent is significant.
Early in the practice of these arts, rolling friction was substituted for sliding friction wherever feasible. Typically, this was accomplished by the use of caged or uncaged rolling elements such as balls or rollers. This development significantly reduced friction and provided a separate load supporting means between the slidably engaged surfaces. However, this development also added significantly to the cost of the machines when compared to the simple boundary lubrication provided by a thin film of oil or grease.
Recently, the use of hard microspheres made of iron, tungsten, nickel and the like and having a diameter of preferably less than 8 microns, as a lubricant, was disclosed in U.S. Pat. No. 3,549,531. This development provided about a 50 percent reduction in the friction of slidably engaged surfaces when compared to that of the simple boundary lubrication. More specifically, when dispersed in an oil or grease these microspheres, of the size disclosed in U.S. Pat. No. 3,549,531, provide a coefficient of friction between two slidably engaged surfaces of about 0.05.